Preheat the oven to 350°F (180°C). For the tart shells, beat the butter and cream cheese in a Classic Batter Bowl until well blended. Add the flour; mix until a soft dough forms.Using the Small Scoop, shape the dough into 1" (2.5-cm) balls. Place the dough balls into the ungreased cups of the Mini Muffin Pan. Dip the Mini Tart Shaper in the flour, and press into the dough with even pressure until the dough rises slightly above the rim of the pan.For the filling, place the butter in a Small Batter Bowl; microwave on HIGH for 30 seconds or until melted. Stir in the brown sugar, egg, and vanilla. Finely chop the pecans using the Food Chopper; add them to the batter bowl contents and mix well.Using the scoop, fill each tart shell with a level scoop of the filling (do not overfill). Bake for 20-25 minutes or until the cookies are light golden brown. Remove the pan from the oven, and let the cookies cool in the pan for 3 minutes. Remove the cookies from the pan to a Stackable Cooling Rack and let them cool completely. Sprinkle with powdered sugar, if desired.